I think the waterproof ones from Nashbar or Performance are a good value; they are both cheap and tough. The non-waterproof ones from Performance (Transit Pro and Transit Epic) are OK too. Between the three of us we used and abused both types on our transamerica tour this summer and they are still in great shape.

We were lucky enough to have mostly dry weather, but the waterproof bags did seem to do a good job for the few rainy days we had.

On the Transit Pro and Epic, I would caution against tightening the mounting strap too tight. It is a bear to get undone if overtightened, but that was my only complaint.

If you plan to ride offroad where there will be much bouncing, buy panniers that will not detach from the rack (Arkel, Ortlieb, maybe a few others). If you are touring on roads, many other less expensive options are available.

For the money I think Axiom Typhoons are the best bet for road touring. Here's one site that compared Ortlieb and Axiom.

I use Nashbar's waterproof panniers. The more common problem with Nashbar's pannier, as reported on crazguyonabike.com is that the hook rivets pull through the backing. I noticed this was a possibility with mine, and I solved that by removing the rivets, adding a little square lexan backing inside the pannier where the hooks mount, and used washers/bolts to hold the hook in place. Now these panniers are tough and work well (I've had them for 5+ years of communting and touring).

However, if I bought new panniers today, I'd try the Axioms Typhoons since I do only road touring, otherwise I would buy the Arkel or Ortlieb panniers.

(If you look around you can find new Axiom Typhoons for about $65 [ebay] to $75 [aebike.com], but many try to sell them for $100+.)